Boron is contained in industrial raw water such as underground water or river water only in an amount of about several tens μg/l. However, since boron is present in water in the form of boric acid, which is an extremely weak acid, boron can only be insufficiently removed by a reverse osmosis membrane or ion exchange resin forming an ultrapure water production apparatus. There is a concern that the apparatus may have a propensity of allowing boron to leak into ultrapure water.
A resin for selectively adsorbing boron prepared by introducing N-methyl-glucamine into a styrene-based resin is commercially available as an adsorbent for efficiently removing a slight amount of boron by utilizing a highly acidic complex formed by boric acid and a polyhydric alcohol. However, this resin for selectively adsorbing boron has only insufficient capability of removing a very slight amount (several ng/l) of boron and allows leakage of boron at the initial stage when the superficial velocity increases.
In order to solve the above shortcoming to the above-mentioned boron absorption resin, Japanese Patent Application Laid-open No. 2000-140631 discloses a resin for selectively adsorbing boron. The resin comprises an anion exchange resin dotted with a compound having at least two phenolic hydroxyl groups and anionic exchange sites. However, since chromotropic acid or the like is dotted on the anion exchange resin via an ionic bond, the resin is unstable to the fluctuation of treated water quality and the compound dotted on the resin is desorbed during use, resulting in a remarkable increase in the effluent TOC load and a reduced adsorption capacity.
Japanese Patent Publication No. 4-49563 discloses a porous ion exchange material comprising an organic porous material has a continuous pore structure comprising macropores and mesopores, the macropores being interconnected with each other forming mesopores in the interconnected parts into which ion exchange groups are introduced. The ion exchange material includes an anion exchange material and is assumed to have the capability of adsorbing and removing boron in principle. However, this adsorption capability is quite limited because boric acid is an extremely weak acid.
An object of the present invention is therefore to overcome the above-mentioned shortcomings of the prior art. Specifically, an object of the present invention is to provide an organic porous material capable of selectively adsorbing boron and having high and stable capability of adsorbing boron, and to provide a boron-removing module and an ultrapure water production apparatus using the organic porous material.